Flotation froth level control



June 14, 1966 J. P. MccARTY ETAL 3,255,882

FLOTATION FROTH LEVEL CONTROL Filed OCt. 15, 1962 MIN( United States Patent O 3,255,882 FLOTATION FROTH LEVEL CONTROL .lames P. McCarty and Bueford W. Taraha, rllucson, Ariz.,

assignors to Duval Sulphur & Potash Company, Houston, Tex., a corporation of Texas Filed Oct. 15, 1952, Ser. No. 230,372 4 Claims. (Cl. 209-1) This invention relates to the control of froth in ilotation separation cells used to separate solids.

In a froth flotation separation system for solids such as minerals a pulp provided by an aqueous mixture is delivered to what is known as a flotation cell. Normally suitable reagents are added to the pulp before it reaches the cell. In the cell a froth is formed on top of the pulp. This froth contains one of the minerals present in the pulp. The froth is skimmed olf of the top of the cell and the skimmed froth and pulp from the cell are thereafter treated to recover the desired minerals.

In the above outlined process and other solid separations considerable difliculty is encountered in maintaining the top of the froth layer at the desired elevation. For instance, changes in the composition of the pulp entering the cell result in different froth conditions, and it is customary to vary the level of pulp in the cell to correctly position the froth so that it `may be readily skimmed from `the top of the cell. In the past a bubble tube has been used for detecting changes in the level of the pulp. Trouble has been encountered using the bubble tube when froth conditions change. It not infrequently resulted in serious overflow of froth or a complete stoppage of froth movement while maintaining a constant pulp level.

An object of this invention is to provide a froth level control system capable of modulating a control valve in such a manner that a continuous steady flow of froth may be withdrawn from the flotation cell under widely varying frothing conditions.

Another object is to provide a froth level control which will maintain a steady flow of froth from a flotation cell "under widely varying frothing conditions Whichis electronic in nature but utlizes a suitable low potential which minimizes danger or discomfort to operating personnel.

Another object is to provide a froth level control as in the preceding object with an economic means of converting the electronic signal from a probe in the froth to a pneumatic signal capable of operating conventional air-operated valves.

Another object is to provide a froth level control capable of modulating a control valve to obtain a continuous steady flow of froth from a flotation cell while frothing conditions vary widely in which the sensitivity of the systern may be readily varied to meet varying conditions.

Other objects, features and advantages of the invention will be apparent from the drawing, the specification, and -the claims.

The single figure in the drawing illustrates schematically the preferred form of this invention as applied to mineral separation.

A mineral separation flotation cell 1tl forms a part of an overall mineral separation circuit of the type which separates minerals by selective flotation. This cell may be of any desired construction, and the invention is usable in the separation of any minerals by the flotation process. For instance, copper may be separated from copper ore. As a further example, potash (potassium chloride) may be separated from sodium chloride. In the conventional 3,25582 Patented .lune 14, 1966 ICC separation process an aqueous pulp 11 is present in the cell and a froth 12 containing one of the minerals oats on the aqueous pulp. This is normally a continuous process and pulp is continuously passed through the cell and froth is continuously formed from this pulp. Suitable skimmers (not shown) may be provided to skim the froth from the top of the cell.

A pulp outlet pipe 13 is connected to the celll 10 below the normal pulp level to provide for removal of the pulp from the cell. The rate of flow of pulp through pipe 13 is controlled by a valve indicated generally at 14.

By this invention there is provided a .new and novel means of controlling the iiow of pulp through valve 14 as a function of the condition of froth 12. This novel means is a'D.C. circuit which includesthe several components to be hereinafter described and which controls the degree of opening of valve 14 in response to froth conditions.

The source of D C. current may be provided in any desired manner. For instance, current may be drawn from a 1Z0-volt A C. system as indicated by the contacts 15 and 16. By positioning a suitable diode 17 in line 18 and connecting line 18 to line 19 through a suitable condenser 21, a D.C. source may be provided. Preferably, a low voltage signal is used and the voltage delivered to the system may be reduced to the desired level by a suitable resistance 22.

The D.C. circuit includes -two parallel branches connected to line 23 in which the resistance: 22 is located. One of these parallel branches is provided by lines 24 and 24a. The other branch is provided by lines 25 and 25a. These two branches are suitably connected to ground at 26 and through line 27 to contact 16 ofthe A.C. supply.

In the parallel branch provided by lines 2S and 25a, a suitable probe 28 is positioned. This probe has a surface area 28a which is in contact with the froth 12. The probe 28 is connected to line 25 and the cell 10 is connected to line 25a to thus position the probe and cell in series in one parallel branch of the circuit.

While the froth 12 is conductive, a useful resistance .to ow of current is exhibited by the froth. This resistance changes as a function of the area of the probe in contact with froth. Obviously as the area increases the resistance decreases. This phenomenon is used by this invention to control operation of valve 14.

Provision is made for manual adjustment of the position of the probe in the froth. Preferably, the probe eX- tends down vertically into the froth and one end terminates within the froth. The probe is shiftable vertically in a clamp 29 to permit the operator to position the probe at the desired elevation inthe froth.

An electric motor is provided in the' other parallel branch provided by conduits 24 and 24a. This electric motor preferably takes the form of a solenoid 31 which is operated by current ilowing in this parallel branch of the circuit. Obviously an electromagnet or other type of electric motor might be used. As is well known from the laws of shunt circuits, a change in resistance in the circuit` including probe 28 will result in a change of flow of current through both parallel branches. This phenomenon is used to effect changes in the position of the core 31a of the solenoid. This change in operation of the motor provided by solenoid 31 is used to control the setting of valve 14.

In accordance with this invention a means is provided to change the sensitivity of the D.C. circuit to meet varying conditions. For this purpose the potentiometer 32 is connected between lines 23, 24 and 25. With the movable contact 32a of the potentiometer connected to line 25, it is obvious tha-t the voltage applied to probe 28 may be selected at will, and thus the sensitivity of the probe circuit may be varied to meet varying conditions.

Any desired means may -be utilized to operate valve 14 in response to operation of motor 31. In the preferred form of this invention a system is provided for converting the electric signal from motor 31 to a pneumatic signal to control the valve 14.

The pneumatic system includes an air supply 33 providing air to a main conduit 34. A flow control means for restricting volume of flow of air through conduit 34 is provided in any desired manner such `as the restrictor 35. Connected to the main conduit 34 downstream of the restrictor are a pair of branch conduits 36 and 37. Conduit 37 conducts air to an air motor 38 which controls or governs valve 14. Conduit 36 terminates in a lnozzle 39. Movable flapper means 40 has a valve means 41 cooperable with the nozzle 39 to control flow of yair through the nozzle. The ilapper 40 may be suitably fulcrumed as indicated at 42, and movement of the tlapper about the fulcrum is controlled by the position of the core 31a of solenoid 31, which core engages the apper.

Operation of the device will be explained beginning with the probe 28 positioned properly to maintain a normal froth overflow and the potentiometer positioned to obtain the desired sensitivity under the conditions of operation. At this time the lower end of the probe isimmersed in froth and a portion of the current is passing through the probe. The balance of the current is passing lthrough the solenoid 31 holding the apper partly away from the nozzle. We may assume the valve 14 to be half open at this time. We may further assume that an upset in the system occurs and the froth level drops in the cell. This `will result in `an increase -in the resistance of the probe circuit. This increase will reduce current flow through the probe and result in an increase in current flow through the solenoid 31. This increase'will pull lthe flapper further away from the nozzle to thus permit an increase in flow of air through the nozzle. This in turn will lower the pressure on the operator 38 for valve 14 and thus move the setting of valve 14 to a more closed position and reduce the ow of pulp `from the cell. This reduced ow will cause the pulp level to increase and thus raise the top of the froth |back up to normal. This will result in decrease in resistance through the probe circuit, which in turn will decrease ow through the solenoid circuit, move the apper toward more closed position, and result in increased flow through valve 14.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made within the scope of the appended claims without departing from the spirit of the invention.

What we claim is:

1. A system for separation of solids by froth flotation comprising,

a flotation cell adapted to contain conductive liquid pulp and a layer of froth on the top of the pulp,

la pulp outlet located rin the cell below the normal pulp level,

a valve governing flow of pulp through said outlet,

and a D.C. circuit controlling said valve including parallel branches in said circuit,

a probe,

means adjustably positioning selected amounts of surface area of said probe in said froth, said probe and cell being connected in one of said parallel branches and providing resistance to ow of current in said one branch as a function of the area of said probe in contact with froth, whereby current flow is varied in accordance with probe area in contact with said froth,

an electric motor in said other parallel branch, said ymotor being operated by the current flow as established `by the probe area -in Contact with said froth,

and means responsive to operation of said motor and controlling said valve.

2. A system for separation of solids'by froth flotation comprising,

a flotation cell adapted to contain conductive liquid pulp and a layer of froth on the top of the pulp,

a pulp outlet located .in the cell below the normal pulp level,

a valve governing ilow of pulp through said outlet,

and a D.C. circuit controlling said Valve including parallel branches in said circuit,

a probe adjustably positioned with one end immersed only in the froth in said cell,

said probe and cell Abeing connected in one of said parallel branches and providing resistance to ow of current in said one branch as a function of the area of said probe in contact with froth, whereby current flow is varied in accordance with the probe area in contact with said froth,

a solenoid in said other parallel branch, and operated by the current flow as established by the probe area in contact with said froth,

and means responsive to the operation of said solenoid controlling said valve.

3. A system for separation of solids by froth flotation comprising,

a otation cell `adapted to contain conductive liquid pulp and a layer of froth on the top of the pulp,

la pulp outlet located `in the cell below the normal pulp level,

a valve governing flow of pulp through said outlet,

and a D C. circuit controlling said valve including, a potentiometer providing parallel branches in said circuit,

`a probe adjustably positioned with one end immersed in the lfroth in said cell,

said probe and cell being connected in one of said parallel `branches and providing resistance to ilow of current *in said one branch as a function of the area of said probe in contact with froth, to thereby control current ow,

a solenoid in said other parallel branch, operated by the current flow as established by the probe area in contact with said froth,

and means responsive to 4the operation of said solenoid controlling said valve.

4. .system for separation of solids by froth flotation comprising,

a flotation cell adapted to contain conductive liquid pulp and a layer of froth on the top of the pulp,

a Lliulp1 outlet located in the cellbelow the normal pulp 'eve an air controlled valve governing flow of pulp through said outlet,

a nozzle,

a source of air under pressure,

a main conduit connected to said source,

flow control means in said conduit controlling the rate of flow of air,

a pair of branch conduits connected to said main conduit downstream of said flow control means,

one of said branch conduits connected to said air controlled valve and the other to said nozzle,

movable apper means including valve means cooperable with said nozzle to regulate air flow through said nozzle,

land a D C. circuit controlling said valve by controlling movement of said apper including,

a potentiometer providing parallel vbranches in said circuit,

3,255,882 5 6 a probe adjustably positioned with one end immersed References Cited by the Examiner sailtli1 phreolotahnn csellld 'lgrg connected in one of said UNITED STATES PATENTS parallel branches and providing resistance to llow 213101298 2/1943 Kuhl et ale- 137392.X of current yin said one branch as a, function of the 5 2149 8,232 2/1950 Andfews IS7- 392 area of said probe in contact with froth to thereby 215731172 10/1951 Ennis et a1- control current ilow, and a solenoid responsive to and operated by the cur- FRANK W' LUTTER Pr'mary Exam'ner' rent ow as established by the probe area in con- HERBERT L. MARTIN, Examiner.

tact with the froth in said other parallel branch con- 10 S WILLIAMS Assistant Examiner ytrolling movement of said apper. 

1. A SYSTEM FOR SEPARATING OF SOLIDS BY FRONT FLOTATION COMPRISING, A FLOTATION CELL ADAPTED TO CONTAIN CONDUCTIVE LIQUID PULP AND A LAYER OF FRONT OF THE TOP OF THE PULP, A PULP OUTLET LOCATED IN THE CELL BELOW THE NORMAL PULP LEVEL, A VALVE GOVERNING FLOW OF PULP THROUGH SAID OUTLET, AND A D.C. CIRCUIT CONTROLLING SAID VALVE INCLUDING PARALLEL BRANCHES IN SAID CIRCUIT, A PROBE, MEANS ADJUSTABLY POSITIONING SELECTED AMOUNTS OF SURFACE AREA OF SAID PROBE IN SAID FROTH, SAID PROBE AND CELL BEING CONNECTED IN ONE OF SAID PARALLEL BRANCHES AND PROVIDING RESISTANCE TO FLOW OF CURRENT IN SAID ONE BRANCH AS A FUNCTION OF THE AREA OF SAID PROBE IN CONTACT WITH FRONT, WHEREBY CURRENT FLOW IS VARIED IN ACCORDANCE WITH PROBE AREA IN CONTACT WITH SAID FROTH, AN ELECTRIC MOTOR IN SAID OTHER PARALLEL BRANCH, SAID MOTOR BEING OPERATED BY THE CURRENT FLOW AS ESTABLISHED BY THE PROBE AREA IN CONTACT WITH SAID FROTH, AND MEANS RESPONSIVE TO OPERATION OF SAID MOTOR AND CONTROLLING SAID VALVE. 